Vim 8.0 was released yesterday, and its new features include background jobs, timers, and asynchronous I/O using channels.
Your description for the g:easytags_async option says that async isn’t the default yet because you’re not sure if it will work reliably for everybody. If you change easytags.vim to use Vim’s new built-in functions such as job_start(), the async tag generation would be more likely to be reliable. Then you could finally make it the default, providing a smoother experience for all users.
You could also add ang:easytags_on_timer option, if you think there would be a demand for it. Though personally I think async would be all I need.
However, you probably shouldn’t remove the current synchronous and hacky-async methods until enough people have had the chance to upgrade to Vim 8.
Doing a very quick scan of the code, it looks like a lot of the logic for generating tags is here. This would be an undertaking looking at the subtle differences of neovim and vim8's approaches to job control / channels.
jalcine
commented
7 years ago 
Taverius
Vim 8.0 was released yesterday, and its new features include background jobs, timers, and asynchronous I/O using channels.
Your description for the
g:easytags_asyncoption says that async isn’t the default yet because you’re not sure if it will work reliably for everybody. If you changeeasytags.vimto use Vim’s new built-in functions such asjob_start(), the async tag generation would be more likely to be reliable. Then you could finally make it the default, providing a smoother experience for all users.You could also add an
g:easytags_on_timeroption, if you think there would be a demand for it. Though personally I think async would be all I need.However, you probably shouldn’t remove the current synchronous and hacky-async methods until enough people have had the chance to upgrade to Vim 8.